On Mon, Aug 21, 2023 at 6:27 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Wed, May 24, 2023 at 1:03 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> >
> > On Mon, May 22, 2023 at 6:20 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> > >
> > > On Fri, 19 May 2023 at 14:57, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> > > >
> > > > Extend the passthrough feature by handling asynchronous IO both for read
> > > > and write operations.
> > > >
> > > > When an AIO request is received, if the request targets a FUSE file with
> > > > the passthrough functionality enabled, a new identical AIO request is
> > > > created. The new request targets the backing file and gets assigned
> > > > a special FUSE passthrough AIO completion callback.
> > > >
> > > > When the backing file AIO request is completed, the FUSE
> > > > passthrough AIO completion callback is executed and propagates the
> > > > completion signal to the FUSE AIO request by triggering its completion
> > > > callback as well.
> > >
> > > Overlayfs added refcounting to the async req (commit 9a2544037600
> > > ("ovl: fix use after free in struct ovl_aio_req")). Is that not
> > > needed for fuse as well?
> > >
> > > Would it make sense to try and merge the two implementations?
> > >
> >
> > Makes sense - I will look into it.
>
>
> Hi Miklos,
>
> Getting back to this.
> Did you mean something like that? (only compile tested)
>
> https://github.com/amir73il/linux/commits/backing_fs
>
> If yes, then I wonder:
> 1. Is the difference between FUSE_IOCB_MASK and OVL_IOCB_MASK
> (i.e. the APPEND flag) intentional?
> 2. What would be the right way to do ovl_copyattr() on io completion?
> Pass another completion handler to read/write helpers?
> This seems a bit ugly. Do you have a nicer idea?
>
Hmm. Looking closer, ovl_copyattr() in ovl_aio_cleanup_handler()
seems a bit racy as it is not done under inode_lock().
I wonder if it is enough to fix that by adding the lock or if we need
to resort to a more complicated scheme like FUSE_I_SIZE_UNSTABLE
for overlayfs aio?
Thanks,
Amir.
